The invention relates to a frame for doors, windows and the like.
The frames of the invention have hollow profile components made out of thermoplastic synthetic resin. The components are welded together by a corner joint, a cross joint or a tee joint. The expression "door frame" and "window frame" as used herein apply not only to the stationary frames of doors and windows, but additionally to moving frames, e.g., frames forming part of the moving part of a window or door.
Attempts have been made to butt-weld hollow profile frame components together by way of the miter-cut surfaces of the corners of the frame. The welding can be a tee joint, in which two or three components are joined together in a T-shape at the welding seam. The components can also be joined in a cross joint by uniting the components to each other at a right angle to form a cross. A third alternative for holding the components is the use of a corner joint, in which the components to be welded are joined at their end surfaces at an angle, usually a right angle.
In known window frames in which the hollow profile components are welded together, the corners of the frame can additionally be foamed. But then, the known frame components of the thermoplastic synthetic resin may under the influence of temperature become subject to considerable stress at the location of the weld, particularly if the components are welded into a tee joint by Y-welding, and the frame corner is formed in part by a cross bar which subdivides the frame (here and in the following paragraphs, the section of a complete frame defined by such a cross bar should be included within the concept of "frames"). Such pressure may be the result of thermal stress, which is promoted when the components are darkly pigmented and therefore more strongly absorb radiation. Generally, the thermal stress develops as a result of thermal expansion of the frame components and possibly at high temperatures due to shrinking processes already initiated by exposure to sunlight. Because of this stress, fissures can develop at the welding seam, especially since the strength of the thermoplastic synthetic resin weakens with rising temperature.